Document edge detection apparatus

Abstract

A document edge detection apparatus that can detect document edges at high speed with good stability and precision, even when the documents have relatively large damaged portions, creases or smears, or have been scanned with a large skew angle.

What is claimed is: 
     
       1. A document edge detection apparatus comprising: (a) edge point detection means for detecting at equal intervals in a primary scanning direction and in a secondary scanning direction perpendicular to the primary scanning direction a plurality of binarized points along at least two edges of a rectangular document image in a two-dimensional image space;   (b) direction vector creation means for creating direction vectors by connecting adjacent pairs of the plurality of binarized edge points detected by the edge point detection means;   (c) counting means for counting each of the direction vectors created by said vector direction means and the number of other direction vectors that have a parallel relationship with vectors included along one document edge in the secondary scanning direction and the number of direction vectors having a perpendicular relationship with vectors included along another document edge in the primary scanning direction;   (d) selection means for retaining the points of the direction vectors with the highest count together with vectors parallel thereto in the secondary scanning direction and eliminating points belonging to other direction vectors having a lower count and retaining the points of the direction vectors having a perpendicular relationship with vectors included along another document edge in the primary scanning direction; and   (e) edge calculation means responsive to points retained by the selection means for each of the scanning directions for obtaining an equation of a straight line for each one of the two edges of the rectangular document image that is coincident with its corresponding document edge.